Relaying Multicast Data in a Wireless Network

ABSTRACT

In order to provide efficient relaying of multicast data in a wireless network, the wireless network comprises a base station and a relay node. The relay node is configured for transmissions on the basis of a radio frame including one or more subframes for unicast transmission and one or more subframes for multicast transmission. In a multicast-only operating mode of the relay node, the base station transmits multicast data to the relay node in one or more subframes which are selectable from the one or more subframes for unicast transmission and the one or more subframes for multicast transmission. The relay node receives the multicast data as transmitted by the base station and transmits the received multicast data in one or more of the subframes for multicast transmission.

TECHNICAL FIELD

The present invention relates to methods of relaying multicast data in awireless network and to corresponding devices.

BACKGROUND

In mobile networks, e.g., according to the 3GPP (3rd GenerationPartnership Project), it is known to use relaying for improving capacityand/or coverage of the network. For example, in 3GPP LTE (Long TermEvolution) relaying was introduced in the Release 10 TechnicalSpecifications (TSs). The general idea of relaying is that a relay node(RN) receives a transmission from a sender and forwards thistransmission to a recipient. For example, a transmission can be receivedfrom a base station, in 3GPP LTE referred to as “evolved Node B” (eNB),and be forwarded to a mobile terminal or other type of user equipment(UE), or vice versa. In 3GPP LTE, a RN communicates with its servingeNB, also referred to as donor eNB, via a backhaul link, and providesaccess to the UEs attached to a relay cell of the RN via an access link.Both the backhaul link and the access link are implemented using the LTEradio interface.

There are basically two different realizations of RNs. First there areRNs, which can separate access and backhaul links sufficiently well,e.g., by means of separated antennas or by means of separated frequencybands, such that they do not have any restrictions on the radiointerface of the access or backhaul link. Second, there are RNs whoseaccess and backhaul links would interfere with each other severely suchthat those RNs require the configuration of access and backhaulsubframes in order to separate the signals in the time domain. Inconfigured backhaul subframes, the RN can communicate with the donor eNBand in access subframes it can communicate with the UEs attached to therelay cell. In downlink (DL) backhaul subframes, in which the RN mayreceive data from its donor eNB, the RN does not transmit the signalsthat are provided in regular subframes, such as reference signals, tothe attached UEs, i.e., UEs in connected mode or UEs in idle mode. Asexplained in 3GPP TS 36.216, Section 5.2, the RN declares the backhaulsubframes as MBSFN (Multimedia Broadcast/Multicast Services over SingleFrequency Network) subframes towards the UEs. This has the purpose ofnot confusing the attached UEs. Accordingly, there are restrictionsconcerning the selection of the backhaul subframes. However, asexplained in 3GPP TS 36.211, Section 6.7, the RN still provides controlinformation, such as the Physical Downlink Control Channel (PDCCH), thePhysical Control Format Indicator Channel (PCFICH), the Physical HybridAutomatic Repeat Request (HARQ) Indicator Channel (PHICH), and referencesymbols in the control region of the subframe, which in MBSFN subframesconsists of the first or first and second Orthogonal Frequency DivisionMultiplexing (OFDM) symbols, see 3GPP TS 36.211, Section 6.7. The PCFICHdynamically provides information about the actual control region size.The remaining OFDM symbols in the MBSFN subframe make up the MBSFNregion. In regular subframes, the OFDM symbols not belonging to thecontrol region are referred to as data region.

Since the RN transmits during the control region of the MBSFN subframe,and may therefore not be able to receive control signaling from itsdonor eNB, a new control channel, i.e., the R-PDCCH was introduced inLTE Release 10 (see 3GPP TS 36.216, Section 5.6.1). This allows thedonor eNB to transmit control information in the data region of asubframe to the RN.

In 3GPP LTE, Multimedia Broadcast/Multicast Services (MBMS) are providedfor efficient delivery of multicast data or broadcast data. Multicastdata are data intended for reception by multiple UEs, and broadcast datacan be considered as a specific case of multicast data which areintended for all UEs capable of receiving the multicast data. In thecontext of MBMS, broadcast data may be received by all connected UEssupporting MBMS, whereas reception of multicast data may be limited to asubgroup of the connected UEs by authentication.

A MBSFN coordinates the transmission of MBMS data, i.e., broadcast dataor multicast data, among a group of eNBs such that all involved eNBsjointly transmit the data, i.e., transmit the same data in asynchronized manner using the same time and frequency resources. From aUE perspective all signals combine over the air resulting in an improvedsignal to interference and noise ratio (SINR). MBMS transmission inMBSFN mode is carried on the Physical Multicast Channel (PMCH) andperformed in the MBSFN region of the MBSFN subframe. In LTE Releases 9and 10, the non-MBSFN region, also referred to as the control region,which consists of the first or first and second OFDM symbols, is used bythe eNB to provide cell-specific control information. The size of thecontrol region is semi-statically configured by the Multi-cell/MulticastCoordination Entity (MCE) for all cells participating in an MBSFN areaand signaled via PCFICH.

For the PMCH, a constant modulation and coding scheme (MCS) has to beset in all cells of the same MBSFN area. Within an MBSFN area, there isno interference between MBMS transmissions of different cells. Thisallows to set an MCS with lower robustness than used for unicast at cellborders. MCS with lower robustness may achieve higher data rates and aresuitable if the coverage is good throughout the MBSFN area (signal tonoise ratio (SNR) above the minimum required for the chosen MCS). If thePMCH MCS robustness is set rather low, more “coverage holes” exist forthe PMCH transmission than for unicast transmissions. It would thereforebe desirable to improve coverage for MBMS transmission in MBSFN mode,e.g., using relaying. However, according to 3GPP TS 36.300, Section15.1, RNs do not support MBMS.

Accordingly, there is a need for efficient techniques which allow forefficient delivery of multicast data and broadcast data also when usingrelaying.

SUMMARY

According to an embodiment of the invention, a method of relayingmulticast data in a wireless network is provided. The wireless networkcomprises at least one RN. The RN is configured for transmissions on thebasis of a radio frame comprising one or more subframes for unicasttransmission and one or more subframes for multicast transmission.According to the method, the RN receives multicast data from a basestation. The multicast data are received by the RN in one or moresubframes which are selectable from the one or more subframes forunicast transmission and the one or more subframes for multicasttransmission. Further, the RN transmits the received multicast data inone or more of the subframes for multicast transmission.

According to a further embodiment of the invention, a method of relayingmulticast data in a wireless network is provided. The wireless networkcomprises at least one RN. The RN is configured for transmissions on thebasis of a radio frame comprising one or more subframes for unicasttransmission and one or more subframes for multicast transmission.According the method, a base station transmits multicast data to the RN.The base station transmits the multicast data in one or more subframeswhich are selectable from the one or more subframes for unicasttransmission and the one or more subframes for multicast transmission.

According to a further embodiment of the invention, a RN for a wirelessnetwork is provided. The wireless network comprises at least one RN. TheRN is configured for transmissions on the basis of a radio framecomprising one or more subframes for unicast transmission and one ormore subframes for multicast transmission. The RN comprises at least oneradio interface for communication with a base station and one or moremobile terminals and a processor for controlling operations of the relaynode. These operations as controlled by the processor comprise:

-   -   receiving, via the at least one radio interface, multicast data        from the base station in one or more subframes which are        selectable from the one or more subframes for unicast        transmission and the one or more subframes for multicast        transmission, and    -   transmitting, via the at least one radio interface, the received        multicast data in one or more of the subframes for multicast        transmission.

According to a further embodiment of the invention, a base station for awireless network is provided. The wireless network comprises at leastone RN. The RN is configured for transmissions on the basis of a radioframe comprising one or more subframes for unicast transmission and oneor more subframes for multicast transmission. The base station comprisesat least one radio interface for communication with one or more mobileterminals and the at least one RN and a processor for controllingoperations of the base station. These operations as controlled by theprocessor comprise:

-   -   the base station transmitting, via the at least one radio        interface, multicast data to the at least one RN in one or more        subframes which are selectable from the one or more subframes        for unicast transmission and the one or more subframes for        multicast transmission.

According to a further embodiment of the invention, a wireless networksystem is provided. The system comprises a base station and a relay nodeRN. The RN is configured for transmissions on the basis of a radio framecomprising one or more subframes for unicast transmission and one ormore subframes for multicast transmission. The base station isconfigured to transmit multicast data to the RN in one or more subframeswhich are selectable from the one or more subframes for unicasttransmission and the one or more subframes for multicast transmission.The RN is configured to receive the multicast data as transmitted by thebase station and transmit the received multicast data in one or more ofthe subframes for multicast transmission.

According to further embodiments, other methods, devices, or computerprogram products for implementing the methods may be provided.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 schematically illustrates a wireless network in which conceptsaccording to embodiments of the invention may be implemented.

FIG. 2 further illustrates structures in a wireless network according toan embodiment of the invention.

FIG. 3 schematically illustrates transmissions in a wireless network inan operating mode of a RN according to an embodiment of the invention.

FIG. 4 schematically illustrates transmissions in a wireless network inan additional operating mode of a RN according to an embodiment of theinvention.

FIG. 5 schematically illustrates a subframe for multicast transmissionas used in an embodiment of the invention.

FIG. 6 schematically illustrates an exemplary configuration of radioframes according to an embodiment of the invention.

FIG. 7 schematically illustrates a further exemplary configuration ofradio frames according to an embodiment of the invention.

FIG. 8 illustrates an information element as used in an embodiment ofthe invention for signaling a radio frame configuration of a RN.

FIG. 9 illustrates a further information element as used in anembodiment of the invention for signaling restrictions of a RN regardingcontrol signaling.

FIG. 10 illustrates a further information element as used in anembodiment of the invention for signaling restrictions of a RN regardingcontrol signaling.

FIG. 11 schematically illustrates structures of a RN according to anembodiment of the invention.

FIG. 12 schematically illustrates structures of a base station accordingto an embodiment of the invention.

FIG. 13 shows a flowchart for illustrating a method according to anembodiment of the invention.

FIG. 14 shows a flowchart for illustrating a further method according toan embodiment of the invention.

DETAILED DESCRIPTION OF EMBODIMENTS

In the following, the invention will be explained in more detail byreferring to exemplary embodiments and to the accompanying drawings. Theillustrated embodiments relate to concepts of multicast data. Theconcepts may be applied in a wireless network according to 3GPP LTE.However, it is to be understood that the illustrated concepts may beapplied in other types of wireless networks as well.

FIG. 1 schematically illustrates an exemplary wireless network in whichconcepts according to embodiments of the invention can be applied.

As illustrated, the wireless network includes a number of base stations110, in particular a first base station (BS1), a second base station(BS2), and a third base station (BS3). Further, the wireless networkincludes a number of RNs 150, in particular a first RN (RN1), and asecond relay node (RN2). In addition, the wireless network includes acontrol node 130, which has the purpose of coordinating multicasttransmissions in the wireless network, which may also include supplyingmulticast data to the base stations 110. This may be accomplished usingwire-based links, illustrated by solid lines. The base stations 110 mayin turn forward the multicast data to their subordinate RNs 150. This isin turn accomplished using radio links, illustrated by dashed lines. Inthe illustrated example, BS1 forwards the multicast data to RN1, i.e.,may be regarded as a donor base station of RN1. BS3 forwards themulticast data to RN2, i.e., may be regarded as a donor base station ofRN2.

A number of mobile terminals or other types of UEs 210, in particular afirst UE (UE1), a second UE (UE2), and a third UE (UE3), are located ina coverage area of the wireless network which allows for receiving themulticast data. This is accomplished using radio links, as illustratedby dashed arrows. In the illustrated example, UE1 receives the multicastdata in a joint transmission from RN1 and BS2, UE2 receives themulticast data in a joint transmission from BS2 and RN2, and UE3receives the multicast data in a transmission from RN2. Here, the term“joint transmission” means that the multicast data are transmitted in asynchronized manner using the same time and frequency resources suchthat the transmitted signals constructively combine over the air. Theterm “multicast data” means data intended for reception by multiple UEsand also includes broadcast data. The term “broadcast data” means aspecific case of multicast data which are intended for all UEs capableof receiving the multicast data.

The wireless network of FIG. 1 may be implemented according to 3GPP LTE.In this case, the transmission of the multicast data may be accomplishedusing MBMS signals in MBSFN transmission mode. Broadcast data may thenbe received by all UEs supporting MBMS, whereas reception of multicastdata may be limited to a subgroup of the UEs, e.g., by authentication.Structures of the wireless network in such an LTE implementation arefurther illustrated in FIG. 2. For the sake of clarity, FIG. 2illustrates only a single base station 110, termed as eNB in accordancewith the 3GPP LTE terminology, a single RN 150, and a single UE 210.However, it is to be understood that multiple base stations, multipleRNs, and/or multiple UEs may be present.

As illustrated in FIG. 2, the control node 130 of FIG. 1 is implementedmultiple entities, namely an MCE 130-1, and an MBMS gateway (MBMS GW)130-2. In addition, FIG. 2 also illustrates a Mobility Management Entity(MME) 140.

Functionalities of the MCE 130-1 include admission control andallocation of radio resources to be used by eNBs and RNs, e.g., the eNB110 and the RN 150, in an MBSFN area for joint transmission of MBMSsignals in MBSFN transmission mode. The MCE 130-1 may also decide on aMCS to be used for the joint transmission. Functionalities of the MBMSGW 130-2 include providing the multicast data to eNBs, e.g., to the eNB110. As illustrated, the MCE 130-1 may be coupled to the MME 140 via aninterface termed as “M3”, the MCE 130-1 may be coupled to the eNB 110via an interface termed as “M2”, and the MBMS GW 130-2 may be coupled tothe eNB 110 via an interface termed as “M1”. Additional functionalitiesof the MCE 130-1 and the MBMS GW 130-2 and properties of the interfacesM1, M2, and M3 may be as defined in 3GPP TS 36.300. As furtherillustrated, the eNB 110 is coupled to the RN 150 via a backhaul link BLwhich may be established via an LTE radio interface termed as “Un”, andthe RN 150 is coupled to the UE 210 via an access link which may beestablished via an LTE radio interface termed as “Uu”. Further detailsconcerning the Un interface and the Uu interface can be found in the3GPP TSs.

FIG. 3 schematically illustrates transmissions in a wireless networkwhen using an operating mode of a RN according to an embodiment of theinvention, e.g., a RN as illustrated in FIGS. 1 and 2. FIG. 3 alsodepicts the RN 150, the donor base station (BS) 110 of the RN 150, and aUE 210. Further, the backhaul link BL between the donor base station 110and the RN 150 as well as the access link between the RN 150 and the UE210 are depicted. The access link is used for multicast transmissions tothe UE 210 and other UEs. In some embodiments, it may also be used forDL unicast transmissions from the RN 150 to the UE 210 or for UL unicasttransmissions from the UE 210 to the RN 150. Next to the RN 150 a radioframe configuration for transmissions by the RN is illustrated. Next tothe donor base station 110 a radio frame configuration for transmissionsby the donor base station 110 is illustrated. Next to the UE 210, aradio frame configuration used for reception by the UE 210 isillustrated. As shown, the radio frame configurations each comprise anumber of subframes 20, 30, 20′, 30′, 20″, 30″. The row denoted by #sfindicates an index of the subframes.

In the radio frame configuration of the base station and in the radioframe configuration of the RN, shading indicates subframes 30, 30′ formulticast transmission. In the above-mentioned 3GPP LTE scenario, thesesubframes may be MBSFN subframes. Absence of shading indicates regularsubframes, i.e., subframes for unicast transmission. In the radio frameconfiguration of the UE, shading indicates subframes 30″ in which the UEis configured for reception of multicast transmissions, e.g., multicasttransmission of MBMS signals in MBSFN transmission mode.

In FIG. 3, transmissions are illustrated by vertical arrows. Solidarrows illustrate multicast transmissions, i.e., transmissions to aplurality of recipients. The multicast transmissions may be accomplishedjointly from the base station 110 to the UE 210 and from the RN 150 tothe UE 210. Dotted arrows illustrate unicast transmissions, i.e.,transmissions to a single recipient, from the base station 110 to the RN150. A dashed arrow illustrates a unicast transmission from the basestation 110 to the UE 210. The unicast transmissions from the donor basestation 110 to the RN 150 have the purpose of providing multicast datafor the multicast transmissions to the RN 150. Further, these unicasttransmissions may also include related control information, e.g., forsynchronizing the multicast transmissions. As can be seen, the donorbase station and the RN 150 jointly transmit the multicast transmissionsto the UE 210. Further, the subframes in the radio frame configurationof the RN 150, which are used by the RN 150 to receive the unicasttransmissions from the donor base station 110, i.e., the backhaulsubframes, can be selected to correspond to a subframe for multicasttransmission, as exemplified by the subframe with index 1, but can alsobe selected to correspond to a subframe for unicast transmission, asexemplified by the subframe with index 5. Accordingly, the selection ofthe backhaul subframes is not restricted. It is therefore possible touse subframes for unicast transmission for receiving the multicast datain the RN 150. This is beneficial when considering that there may beonly a limited number of subframes which can be configured for multicasttransmission. For example, in 3GPP LTE at most six out of ten subframesof a radio frame can be configured as MBSFN subframes. Moreover, thereare no unicast transmissions from the RN 150 to the UE 210, i.e., theoperation as illustrated in FIG. 3 corresponds to an operating mode inwhich the RN 150 relays multicast data, but no unicast data. The latteravoids confusion of the UE 210 due to the unicast transmissions from thedonor base station to the RN 150. In particular, the RN 150 can beimplemented to appear transparent to the UE 210, because the UE 210receives unicast transmissions only from the base station, and the jointmulticast transmissions combine over the air so that their origin is notseparable by the UE. There is no need for the RN 150 to declare thebackhaul subframes as subframes for multicast transmission, therebyincreasing the number of subframes for multicast transmission which areactually available for multicast transmissions. For example, inexemplary radio frame configurations of FIG. 3, the subframe with index1 would not be available for multicast transmissions.

Accordingly, an embodiment of the present invention is based onproviding a RN with an operating mode in which the relay node relaysmulticast data, but no unicast data. This operating mode is herein alsoreferred to as a multicast-only operating mode. In the above-mentioned3GPP LTE scenario, the RN may forward MBMS data only. In this case themulticast-only operating mode may also be termed as MBMS only operatingmode. Since this kind of relay operation does not forward unicast data,the RN does not need to create its own relay cell, and the RN does nothave to configure subframes, in which the eNB may transmit the backhaultraffic to the RN, as MBSFN subframes. Hence, the donor eNB is free touse any subframe for backhauling and it can use the regular PDCCH/PDSCHstructure instead of the R-PDCCH for backhauling. Such a 3GPP LTE RNwith MBMS-only operating mode can use all of the available MBSFNsubframes for joint MBMS transmission within an MBSFN area.

Towards UEs, the RN with MBMS-only operating mode is invisible inregular subframes. In MBSFN subframes it would jointly transmit MBMSdata. However, during joint MBSFN transmissions such a RN would betransparent since all MBMS signals transmitted in the MBSFN combine overthe air and are not separable. Regarding the uplink (UL), a RN inMBMS-only operating mode does not have to be capable of receiving uplinksignals from UEs.

In some embodiments, if less MBSFN subframes are needed for thetransmission of MBMS data, while unicast traffic increases in thecoverage area of the RN, the RN may dynamically switch to a mixedoperating mode in which the RN it creates its own cell to serve UEs,i.e., also forwards unicast data, while MBSFN transmission of MBMSsignals is still supported. If the MBMS traffic load requires the use ofall or at least a majority of the MBSFN subframes, the RN may switchback to the MBMS-only operating mode. Transmissions in such anadditional operating mode of the RN according to an embodiment of theinvention are further illustrated in FIG. 4. As mentioned above, thisadditional operating mode is herein referred to as a mixed operatingmode.

As can be seen from FIG. 4, which is generally similar to FIG. 3, in themixed operating mode the RN 150 forwards both multicast data and unicastdata. As in FIG. 3, the reception of the multicast data to be forwardedin the RN 150 occurs via unicast transmissions from the donor basestation, illustrated by dotted arrows. However, as exemplified in thesubframes with index 1 and 6, these unicast transmissions areaccomplished in backhaul subframes corresponding to subframes formulticast transmissions 30 in the radio frame configuration of the RN150. As further illustrated in FIG. 4 also the reception of unicast datato be forwarded in the RN 150 occurs via unicast transmissions from thedonor base station 110, illustrated by a dashed arrow. Again, theseunicast transmissions are accomplished in backhaul subframescorresponding to subframes for multicast transmission 30 in the radioframe configuration of the RN 150, like exemplified in the subframe withindex 3. The transmission of the unicast data from the RN 150 to the UE210, again illustrated by a dashed arrow, is accomplished in subframesfor unicast transmission, like exemplified in the subframe with index 4.As mentioned above, in the 3GPP LTE scenario the backhaul subframes maybe MBSFN subframes. This behavior is compatible with the requirements of3GPP TS 36.216, so that the RN is capable of building a relay cell forserving UEs in unicast transmissions. At the same time, the RN can alsosupport MBSFN transmission of MBMS signals. As can be seen from theillustration of FIG. 4, in the mixed operating mode less of thesubframes for multicast transmission are available for multicasttransmissions towards the UEs since some of these subframes are neededas backhaul subframes for receiving data from the donor base station.

According to an embodiment of the invention, the RN may support themulticast-only operating mode, but not the mixed operating mode.Alternatively, the RN may support both the multicast-only and the mixedoperating mode. As mentioned above, in the multicast-only operating modethe RN may be transparent to the UEs, such that it does not have tocreate its own relay cell, which makes it less restrictive regarding thebackhaul link to the donor base station. In the mixed operating mode,the RN may create its own relay cell to serve UEs, but may stillparticipate in joint multicast transmissions of multicast data.

The RN supporting both the multicast-only and the mixed operating modecould be statically configured, e.g., by operations and maintenanceprocedures, when to operate in the multicast-only operating mode andwhen to operate in the mixed operating mode. Further, the RN could alsodynamically switch between the multicast-only operating mode and themixed operating mode, e.g., depending on the amount radio resourcesneeded for multicast transmissions and/or for unicast transmissions toUEs in the coverage area of the RN.

In the mixed operating mode, only a subset of the subframes would beconfigured as subframes for multicast transmission. However, a largeramount of radio resources may be needed for multicast transmissions.This may trigger the RN to switch from the mixed operating mode to themulticast-only operating mode. When switching from the mixed operatingmode to the multicast-only operating mode, also a handover of UEsinvolved in transmission of unicast data and served by the RN may beinitiated. The handover may for example be to the donor base station, tosome other base station, or to some other RN.

For example, when assuming the structure according to 3GPP LTE asillustrated in FIG. 2, the MCE 130-1 may request the allocation of alarger amount of radio resources to multicast transmissions, such thatmost MBSFN subframes would be needed for MBSFN transmission of MBMSdata, while the number of MBSFN subframes remaining to be used asbackhaul subframes would not be sufficient to support both MBMS andunicast transmission. Active UEs that are involved in unicasttransmission and served by the RN would be in connected mode. The RNcould then initiate a forced handover of these UEs to another suitablecell, e.g., served by the donor eNB, by another eNB, or by another RN.UEs in idle mode may be moved to another cell. This could be achieved bypaging these UEs, thereby moving them to connected mode such that aforced handover can be initiated. A further possibility to avoid thatUEs in idle mode camp on the RN cell would be to set a very low priorityto that cell. The RN may then stop transmitting in the regular subframesand providing reference signals that UEs use for measurements, therebydeactivating the relay cell of the RN. The RN may further informs thedonor eNB that it has switched to the MBMS-only operating mode, suchthat it can receive backhaul data in basically any subframe that is notused for MBSFN transmission and that the use of the R-PDCCH is notneeded any more.

If in the multicast-only operating mode a larger amount of radioresources is needed for unicast transmissions or the amount of radioresources needed for multicast transmissions is below a threshold, thismay trigger the RN to switch from the multicast-only operating mode tothe mixed operating mode, thereby making additional radio resourcesavailable for unicast transmissions and/or improving coverage forunicast transmissions.

For example, when assuming the structure according to 3GPP LTE asillustrated in FIG. 2, if the MCE 130-1 releases radio resourcesallocating less MBSFN subframes for MBMS transmission, such that thenumber of MBSFN subframes would be sufficient to carry backhaul data forboth unicast and MBMS transmission, a RN may decide to switch from theMBMS-only operating mode to the mixed operating mode. More optimizedsolutions could also be applied, e.g., unicast activity in the coveragearea of the RN could be monitored using either measurements orinformation from the donor eNB. When the RN switches from the MBMS-onlyoperating mode to the mixed operating mode, it may have to inform thedonor eNB that it has switched to the mixed operating mode so that thiscan be taken into account by the eNB, e.g., by selecting the backhaulsubframes as explained in connection with FIG. 4. Then, the RN may starttransmitting data in regular subframes and transmitting referencesignals and system or control information to create its own cell andserve UEs.

FIG. 5 schematically illustrates a subframe for multicast transmissionas used in an embodiment of the invention. In particular, theillustrated structure of the subframe corresponds to a MBSFN subframe asused in the above-mentioned 3GPP LTE scenario. The illustration showsthe time and frequency resources of the subframe in form of blocksarranged along a time axis, denoted by t, and a frequency axis, denotedby f.

As illustrated, the subframe for multicast transmission includes a firstslot S1 and a second slot S2, each consisting of six OFDM symbols. InFIG. 5, a symbol index is denoted by #sym. In the illustrated example,the first two OFDM symbols of the subframe, i.e., the OFDM symbols withindex 0 and 1 in the first slot S1, form a control region CR of thesubframe. The remaining OFDM symbols of the subframe, i.e., the OFDMsymbols with index 2 to 5 in the first slot S1 and the OFDM symbols withindex 0 to 5 in the second slot S2, form a multicast region of thesubframe, in the illustrated example of an MBSFN subframe also referredto as MBSFN region.

Each OFDM symbol of the subframe includes a cyclic prefix CP, CP′. Forthe OFDM symbols of the multicast region MR, typically a length of thecyclic prefix CP′ is used which is extended as compared to the length ofthe cyclic prefix for the OFDM symbols of the control region. With theextended cyclic prefix CP′, it can be taken into account that the UEtypically receives the joint MBSFN transmission in the multicast regionfrom various sources, which may have different distances to the UE.According to 3GPP TS36.211 Table 6.12-1, the cyclic prefix CP of thefirst OFDM symbol of the control region CR, i.e., the OFDM symbol withindex 0 in the first slot S1, has a length of about T_(CP0)=5.2 μs, thecyclic prefix CP of the second OFDM symbol of the control region CR,i.e., the OFDM symbol with index 1 in the first slot S1, has a length ofabout T_(CP0)=4.7 μs, and the cyclic prefixes CP′ of the OFDM symbols inthe multicast region MR each have an extended length of aboutT_(CP-e)=16.7 μs.

The OFDM symbols in the subframe are arranged according to a regulargrid with a basic length of 1 s/12=(T+T_(CP-e)), where T denotes thelength of an OFDM symbol and is about T=66.7 μs. All OFDM symbols withinthe MBSFN region are transmitted according to this grid, whereas theOFDM symbols within the control region CR use the shorter cyclic prefixCP and are thus shorter than two OFDM symbols using the extended cyclicprefix CP′ of the multicast region. Thus, there is a gap G between thelast OFDM symbol of the control region CR and the first OFDM symbol ofthe multicast region. The length of the gap G depends on whether one ortwo OFDM symbols are configured for the control region CR. In theexample of FIG. 2, in which the control region of the subframe includestwo OFDM symbols, the length of the gap G may be about 13.5 μs.

When the RN uses the above-mentioned MBMS-only operating mode, thecontrol region CR may carry DL control signaling from the donor eNB,which can be received by the RN and also by UEs, whereas the multicastregion MR may carry the actual MBSFN transmission by the RN, andtypically also by the donor eNB. However, it is to be understood thatthe control region CR may also be used to convey other types of controlinformation.

In some embodiments, if the RN using the MBMS-only operating modeparticipates in the MBMS transmission, it will transmit the PMCH in themulticast region, i.e., operate in a transmit (Tx) mode. Before andafterwards the RN will monitor control information, e.g., uplink grantsor downlink assignments, provided by the donor eNB, i.e., operate in areceive (Rx) mode. The Rx-Tx switching is performed between the controlregion CR and the multicast region MR, and a Tx-Rx switching isperformed between the multicast region and the control region CR of thesubsequent subframe. In the example of FIG. 5, Tx-Rx switching wouldtherefore occur before the first OFDM symbol of the subsequent subframeand after the last OFDM symbol of the subframe for multicasttransmission, and Rx-Tx switching would occur between the last OFDMsymbol of the control region and the first OFDM symbol of the multicastregion MR, i.e., between the OFDM symbol with index 1 and the OFDMsymbol with index 2, which is at the location of the gap G. The gap Gmay therefore be used for the Rx-Tx switching. If the Rx-Tx switchingcannot be done during the gap G switching time could alternatively betaken from the multicast region MR, from the control region CR or fromboth. Similarly, if the Tx-Rx switching cannot be done between the lastOFDM symbol of the multicast region MR and the first OFDM symbol of thecontrol region of the subsequent subframe, e.g., during some gap formedat this position, switching time could be taken from the multicastregion MR, from the control region CR of the subsequent subframe, orfrom both.

In the above examples, if the switching time is taken from the controlregion CR, this may result in the RN not being able to completelyreceive a OFDM symbol of the control region CR, which may result in higherror probability. If the switching time is taken from the multicastregion MR, this may result in the RN not being able to start themulticast transmission in time or being forced to end the multicasttransmission early. In other words, if the switching time is taken fromthe multicast region MR, the RN may need to start its participation in ajoint multicast transmission a bit later and/or to end its participationin a joint multicast transmission a bit earlier. If the switching timeis taken from both the control region CR and the multicast region MR,both of the above effects may occur.

The effect of the switching time depends on various factors, e.g., onthe length of the control region CR, but also where the multicast regionMR starts. If for example the control region CR has a length of one OFDMsymbol and the multicast region MR starts at the third OFDM symbol, atleast one entire symbol can be used for Rx-Tx switching.

Due to the above-mentioned Rx-Tx switching and Tx-Rx switching, thedonor eNB may have some restrictions concerning the use of the controlregion CR for the transmission of control information to the RN.Accordingly, some embodiments of the invention include that the RNprovides an indication of such restrictions to the eNB. This will befurther explained in the following.

FIG. 6 schematically illustrates an exemplary configuration of radioframes as used by a RN according to an embodiment of the invention. Morespecifically, FIG. 6 illustrates an exemplary sequence of a first radioframe RF1 and a subsequent second radio frame RF2. Similar as in FIG. 5,the illustration shows time and frequency resources in the form ofblocks arranged along a time axis, denoted by t, and a frequency axis,denoted by f. Along the time axis, the radio frames RF1, RF2 aresubdivided into a sequence of subframes 20, 30. An index of thesubframes is denoted by #sf. The subframes 20 correspond to subframesconfigured for unicast transmission, and the subframes 30 correspond tosubframes configured for multicast transmission. The subframes 30 mayeach have a structure as illustrated in FIG. 5. As further illustrated,each of the subframes includes a control region, indicated by dottedshading, and a multicast region, indicated by hatched shading. Positionsat which there may be restrictions concerning the transmission ofcontrol information to the RN using the control region of a subframe formulticast transmission are marked by flash symbols. In the 3GPP LTEscenario, the radio frame configurations of FIG. 6 correspond to amaximum configurable number of MBSFN subframes when assumingtransmissions using frequency division duplexing (FDD) between DL andUL.

FIG. 7 shows a further exemplary configuration of radio frames as usedby a RN according to an embodiment of the invention. The illustration ofFIG. 7 is generally similar to that of FIG. 6. However, in the 3GPP LTEscenario, the radio frame configurations of FIG. 7 correspond to amaximum configurable number of MBSFN subframes when assumingtransmissions using time division duplexing (TDD) between DL and UL. Ascan be seen, this results in less of the subframes 20, 30 beingconfigurable for multicast transmissions.

As can be seen from the examples of FIGS. 6 and 7, at most eightsubframes for FDD and seven subframes for TDD will have restrictionsconcerning the transmission of control information. In FIG. 6, the RNusing the multicast-only operating mode has no restrictions at least insubframes with index 0 and 5, and in FIG. 7 the RN using themulticast-only operating mode has no restrictions at least in subframeswith index 1, 2, and 6.

To let the donor base station know the restrictions concerning thetransmission of control information to the RN using control region ofthe subframes for multicast transmission configured in the RN operatingin the multicast-only mode, the RN may provide an indication to thedonor base station. For example, such an indication could include thepositions of subframes marked by flash symbols in FIG. 6 or 7. The donorbase station could then apply suitable mechanisms to take into accountthe restrictions.

For example, the donor base station could choose not to transmit anycontrol information in the indicated subframes. In the 3GPP LTEscenario, the donor base station could refrain from transmitting thePDCCH for the RN. This may be beneficial if the switching time is solong that the error probability is very high and the PDCCH will not bedetectable or decodable.

The donor base station could also adapt the way of transmitting thecontrol information in the indicated subframes.

For example, the donor base station could also issue control informationwhich is valid for more than one subframe, thereby avoiding transmissionof control information in at least some of the indicated subframes,e.g., by using semi-persistent scheduling to issue a semi-persistent DLassignment which is valid for more than one subframe. When usingsemi-persistent scheduling in the 3GPP LTE scenario, the donor eNB cantransmit data on the PDSCH of subframes which do not contain the PDCCH.Even the use of dynamic inter-subframe scheduling may be considered.Since the traffic load for the delivery of data for multicasttransmissions, e.g., for MBSFN transmissions, can be rather static,semi-persistent scheduling may be an appropriate choice.

If in the 3GPP LTE scenario the donor eNB and the RN support carrieraggregation, the eNB could also use cross-carrier scheduling if multiplecarriers are available. In this case the donor eNB could transmit thePDCCHs intended for the MBSFN subframe and its subsequent subframe on adifferent component carrier. If the component carriers are sufficientlyisolated, e.g., by large separation in the frequency domain, the Rx-Txand Tx-Rx switching on one carrier does not affect the transmission andreception on another carrier.

In the 3GPP LTE scenario, the donor eNB could choose a higher PDCCHaggregation level for the RN, e.g., by lowering the code rate, which inturn increases the robustness of the PDCCH transmission. This may bebeneficial if the switching time takes away only a small fraction of thePDCCH region and the resulting error probability is acceptable.

In the 3GPP LTE scenario, the donor eNB could also choose to transmitthe PDCCH on a position where most parts of the PDCCH, i.e., mostResource Element Groups (REGs), are located in a OFDM symbol which canbe received completely by the RN. In the MBSFN subframe, most REGs canexpected to be located in the beginning of the control region and in thesubframe following the MBSFN subframe they can expected to be at the endof the control region.

In the 3GPP LTE scenario, the donor eNB could also use the R-PDCCH totransmit the control information. Since the R-PDCCH is not located inthe normal PDCCH control region, but it is transmitted in the dataregion of a subframe, the donor eNB can send control information to theRN with MBMS-only operating mode at least in subframes that are not usedfor MBMS transmission, e.g., the subframes following the MBSFNsubframes.

In the 3GPP LTE scenario, other physical channels that might be affectedare the PHICH and the PCFICH, which are transmitted in the very first DLsymbol of any subframe. If the donor eNB is aware of the restrictions ofa RN using the MBMS-only operating mode it could also avoid sendingfeedback via the PHICH and instead send an UL grant with a non-toggledNew Data Indicator (NDI) bit (indicating a negative acknowledgement), itcould send an UL grant with a toggled NDI bit (indicating anacknowledgement) or it could send nothing (indicating anacknowledgement). The donor eNB could also avoid modifying the size ofthe control region compared to the previous MBSFN subframe. Suchmodifications may be signaled via the PCFICH. Then the RN using theMBMS-only operating mode would apply the same size of the control regionas in the MBSFN subframe before. If possible, the donor eNB might alsouse higher layer signaling to modify the size of the control region inthe MBSFN subframes.

If in the 3GPP LTE scenario switching time is taken from the MBSFNregion, this may result in the RN using the MBMS-only operating modejoining the MBSFN transmission a bit later and/or stopping it stop a bitearlier. Here, the Rx-Tx switching is typically less critical since, asexplained in connection with FIG. 5, there is a gap between the controlregion and the MBSFN region. However, the first OFDM symbol of the MBSFNregion carrying the PMCH might be used for reference signals. Since thetransmission of reference signals may be critical, it should be avoidedto take the switching time from this OFDM symbol.

Further, in the 3GPP scenario the donor eNB may be able to configure thecontrol region at the beginning of the MBSFN subframe to a certaindegree, e.g., using the PCFICH, such that the donor eNB and the RN usingthe MBMS-only operating mode use different control region sizes. If thenon-MBSFN region as configured for the eNB by the MCE consists of twoOFDM symbols, the donor eNB could configure the RN to use asingle-symbol control region in order to increase the gap between thecontrol and the MBSFN region. Thus, an entire OFDM symbol could be usedfor Rx-Tx switching.

In the following, ways of how the donor base station may become aware ofthe restrictions concerning the transmission of control information tothe RN operating in the multicast-only mode will be discussed in moredetail.

In some cases, the donor base station may already have information fromwhich the presence of such restrictions can be derived. For example, ifin the 3GPP LTE scenario the donor eNB is part of the same MBSFN area asthe RN, it will know the MBSFN subframes actually used for MBSMtransmission using the MBMS Scheduling Information received from the MCE130-1 via the M2 interface and from the timestamps in the MBMS datapackets received from the MBMS GW 130-2 via the M1 interface. Then itcan derive in which subframes the RN may have restrictions concerningthe transmission of control information, e.g., in MBSFN subframes thatare actually used for MBMS transmission and subframes that follow theMBMS transmission.

In these cases, it may be sufficient for the donor base station toreceive an indication from the RN that it uses the multicast-only mode.For example, this indication be signaled by an indicator bit in asignaling message from the RN to the donor base station.

In other cases the donor base station may not have information availablefrom which the presence of such restrictions can be derived. Forexample, in the 3GPP LTE scenario the donor eNB may be not aware of theMBSFN subframes actually used for MBSFN transmission at the RN becauseit is not part of the same MBSFN area.

In these cases, explicit signaling from the RN to the donor base stationmay be used to indicate either the subframes configured for multicasttransmissions, the subframes to be actually used for multicasttransmissions, or the subframes in which the RN has restrictionsregarding the transmission of control information. If such explicitsignaling is not received, donor base station may assume that allsubframes which can be configured for multicast transmissions areactually to be used for multicast transmissions by the RN.

The options of indicating the subframes to be actually used formulticast transmissions, or the subframes in which the RN hasrestrictions regarding the transmission of control information have thebenefit that the donor base station may also use this indication forderiving which of the subframes configured for multicast transmissionscould be used as backhaul subframes for transmitting multicast data tothe RN.

In the 3GPP LTE scenario, the subframes configured for multicasttransmission, i.e., the reserved MBSFN subframes could be indicated bythe RN to the eNB by reusing an information element termed as“MBSFN-SubframeConfig” and defined by 3GPP TS36.331, Section 6.3.7. Suchan information element is illustrated in FIG. 8. In particular, thepositions of the reserved MBSFN subframes could be indicated by the “BITSTRING” field in which each bit corresponds to a position in a radioframe, and setting the bit can be used to indicate that the subframe inthe corresponding position is a reserved MBSFN subframe.

As mentioned above, the positions of subframes with restrictionsconcerning the signaling of control information can also be explicitlysignaled from the RN to the donor base station. For example, thepositions of the subframes in which the RN will perform theabove-mentioned Rx-Tx switching and/or Tx-Rx switching can be indicated.In the 3GPP LTE scenario, for example the information element termed as“MBSFN-SubframeConfig” could be extended for this purpose to include abit string of one octet per radio frame. In this bit string, each bitcorresponds to a position in a radio frame, and setting the bit can beused to indicate whether the subframe in the corresponding position hasrestrictions concerning the transmission of control information or not.

In the 3GPP LTE scenario, when assuming high load for MBMS transmission,it is also possible to omit the fields “radioframeAllocationPeriod” and“radioframeAllocationOffset” from the information element of FIG. 6 andonly indicate the subframes within the “BIT STRING” of the “oneFrame” or“fourFrame” structures as illustrated in FIG. 9, or to only use the“oneFrame” structure as illustrated in FIG. 10, each bit of the “BITSTRING” field indicating the subframes in which the RN as restrictionsconcerning the transmission of control information.

FIG. 11 further illustrates structures of a RN 150 according to anembodiment of the invention. The RN 150 may implement theabove-described functionalities of relaying multicast data and supportat least the multicast-only operating mode as explained above.Optionally, the RN 150 may additionally support the mixed operating modeas explained above.

In the illustrated example, the RN 150 includes a backhaul interface 152for communication with the donor base station and an access interface153 for communication with UEs. The backhaul interface 152 and theaccess interface 153 may be implemented by a single physical radiointerface, e.g., including corresponding shared antennas, receivers,and/or transmitters, or may be implemented by separate physical radiointerfaces, e.g., by using dedicated antennas, receivers, and/ortransmitters. In the 3GPP LTE scenario, the backhaul interface maycorrespond to the Un interface. In the concepts as described herein, thebackhaul interface 152 may in particular be used to receive multicastdata to be forwarded by the RN. In addition, it may also be used to sendindications to the donor base station, e.g., an indication that the RN150 is using the multicast-only operating mode as explained above and/oran indication of restrictions regarding the transmission of controlinformation to the RN 150. In addition, the backhaul interface may alsobe used to receive control information, e.g., scheduling information orsynchronization information for joint transmissions of multicast data.The backhaul interface 152 may be used for other purposes as well, e.g.,for receiving DL unicast data to be forwarded by the RN 150 to a UE orfor forwarding UL unicast data received from a UE to the donor basestation when the RN 150 is in the mixed operating mode, if supported.The access interface 153 may in particular be used to send multicasttransmissions with the received multicast data to UEs. Optionally, ifthe RN 150 additionally supports the mixed operating mode, the accessinterface 153 may also be used to send unicast data to UEs, to receiveunicast data from UEs, to send control information to UEs and/or receivecontrol information from UEs, and to send reference signals to UEs.

Further, the RN 150 includes a processor 154 coupled to the backhaulinterface 152 and the access interface 153, and a memory 155 coupled tothe processor 154. The memory 155 may include a read-only memory (ROM),e.g., a flash ROM, a random-access memory (RAM), e.g., a Dynamic RAM(DRAM) or static RAM (SRAM), a mass storage, e.g., a hard disk or solidstate disk, or the like. The memory 155 includes suitably configuredprogram code to be executed by the processor 154 so as to implement theabove-described functionalities of relaying multicast data. Morespecifically, the memory 155 may include a multicast transmission module156 so as to implement the above-described forwarding of multicast data.If the RN 150 supports the mixed operating mode, the memory 155 may alsoinclude a unicast transmission module 157 so as to implement forwardingof unicast data in the mixed operating mode as explained above. Further,the memory 155 may also include a control module 158 so as to implementvarious control functionalities, e.g., configuration of radio frames,sending of indications to the donor base station, and/or switchingbetween operating modes.

It is to be understood that the structure as illustrated in FIG. 11 ismerely schematic and that the RN 150 may actually include furthercomponents which, for the sake of clarity, have not been illustrated,e.g., further interfaces. Also, it is to be understood that the memory155 may include further types of program code modules, which have notbeen illustrated. According to some embodiments, also a computer programproduct may be provided for implementing concepts according toembodiments of the invention, e.g., a medium storing the program code tobe stored in the memory 155.

FIG. 12 further illustrates structures of a base station 110 accordingto an embodiment of the invention. The base station 110 may implementthe above-described functionalities of relaying multicast data. Asmentioned above, the base station may correspond to an eNB according to3GPP LTE.

In the illustrated example, the base station 110 includes a radiointerface 112 for communication with RNs and UEs, and a backhaulinterface 113 for communication with the network, e.g., with the controlnode 130 as illustrated in FIG. 1 or the MCE 130-1 and the MBMS GW 130-2as illustrated in FIG. 2. The radio interface 112 may be implemented toinclude, e.g., corresponding antennas, receivers, and/or transmitters.In the 3GPP LTE scenario, the radio interface operate as the Uninterface when the base station 110 communicates with a RN and mayoperate as the Uu interface when the base station directly communicateswith a UE. The backhaul interface 113 is typically a wire-basedinterface. For example, the backhaul interface may implement the M1 andM2 interfaces as shown in FIG. 2. In the concepts as described herein,the backhaul interface 113 may in particular be used to receivemulticast data to be transmitted by the base station 110 to UEs or to beforwarded by the base station 110 to a subordinate RN. The radiointerface 112 may in turn be used for forwarding the multicast data tothe RN and to accomplish multicast transmissions of the multicast datato UEs. In addition, it may also be used to receive indications from theRN, e.g., an indication that the RN is using the multicast-onlyoperating mode as explained above and/or an indication of restrictionsregarding the transmission of control information to the RN. Inaddition, the radio interface 112 may also be used to send controlinformation to UEs or RNs, e.g., scheduling information orsynchronization information for joint transmissions of multicast data.The radio interface 112 may be used for other purposes as well, e.g.,for receiving UL unicast data forwarded by a RN 150 or for sending DLunicast data to the RN when the RN is in the mixed operating mode. Theradio interface 112 may also be used to send unicast data to UEs, toreceive unicast data from UEs, to send system or control information toUEs and/or receive control information from UEs, and to send referencesignals to UEs.

Further, the base station 110 includes a processor 114 coupled to theradio interface 112 and the backhaul interface 113, and a memory 115coupled to the processor 114. The memory 115 may include a read-onlymemory (ROM), e.g., a flash ROM, a random-access memory (RAM), e.g., aDynamic RAM (DRAM) or static RAM (SRAM), a mass storage, e.g., a harddisk or solid state disk, or the like. The memory 115 includes suitablyconfigured program code to be executed by the processor 114 so as toimplement the above-described functionalities of the donor base stationwhen relaying multicast data. More specifically, the memory 115 mayinclude a relay control module 116 so as to implement various controlfunctionalities, e.g., configuration of radio frames, processing ofindications from the RN, appropriate control of transmissions of controlinformation taking into account restrictions at the RN. Further, thememory 115 may include a multicast/unicast transmission module 117 so asto implement the above-described forwarding sending multicast data andsending and/or receiving unicast data.

It is to be understood that the structure as illustrated in FIG. 12 ismerely schematic and that the base station 110 may actually includefurther components which, for the sake of clarity, have not beenillustrated, e.g., further interfaces. For example, the base station 110may also comprise multiple radio interfaces which are similar to theradio interface 112, e.g., to allow for using separate physicalinterface structures for communicating on the one hand with UEs and onthe other hand with RNs, or for allowing to use multipath transmissiontechniques. Also, it is to be understood that the memory 115 may includefurther types of program code modules, which have not been illustrated.According to some embodiments, also a computer program product may beprovided for implementing concepts according to embodiments of theinvention, e.g., a medium storing the program code to be stored in thememory 115.

FIG. 13 shows a flowchart illustrating a method according to anembodiment of the invention. The method may be used to implement theabove concepts of relaying multicast data in a RN of a wireless network,e.g., in the RN 150 as explained above. When implementing the method,the RN is configured for transmissions on the basis of a radio framecomprising one or more subframes for unicast transmission and one ormore subframes for multicast transmission. If the wireless network isimplemented according to 3GPP LTE, the subframes for multicasttransmission may be MBSFN subframes. The subframes for unicasttransmission may be regular subframes.

At step 1310, multicast data are received by the relay node, e.g., usingthe backhaul interface 152 of FIG. 11. The subframes for receiving themulticast data, herein referred to as backhaul subframes, are selectablefrom the subframes for unicast transmission and the subframes formulticast transmission. The multicast data are received from a donorbase station, e.g., a base station 110 as explained above. If thewireless network is implemented according to 3GPP LTE, the donor basestation may be an eNB. The multicast data are typically intended formulticast transmissions to UEs. These multicast transmissions by the RNmay be performed jointly with a base station, e.g., the donor basestation or some other base station, and/or with at least one other RN.

At optional step 1320, the RN receives synchronization information fromthe donor base station. The synchronization information may be used bythe RN when performing multicast transmissions jointly with a basestation, e.g., the donor base station, or some other base station. Thesynchronization information may for example define an allocation oftransport channels, e.g., of the PMCH, to subframes and/or session startinformation. Here, it is to be understood that the synchronizationinformation may be transmitted in dedicated messages and/or betransmitted together with the multicast data of step 1310, e.g., in theform of time stamps included in the multicast data.

At optional step 1330, the RN receives control information, e.g., DL orUL scheduling information such as assignments of time and frequencyresources, information on a coding scheme to be used, and/or informationon a Tx power to be used for transmissions on the backhaul link. Thesubframes for multicast transmission may each comprise a control regionand a multicast region. The control information may be received in acontrol region of a subframe for multicast transmission, in particularin a subframe used by the RN for the transmission of the multicast datafrom the relay node, i.e., for a multicast transmission to UEs. In thiscase a time period for switching between receiving the controlinformation and transmitting the received multicast data may extend onlyin the control region, only in the multicast region, or both in thecontrol region and the multicast region.

At step 1340, the RN transmits the received multicast data in one ormore of the subframes for multicast transmission. As mentioned above,this may be performed jointly with a base station, e.g., the donor basestation or some other base station, and/or with at least one other RN.If the wireless network is implemented according to 3GPP LTE, the jointtransmission may be implemented by transmitting MBMS signals in MBSFNtransmission mode.

In some embodiments, the RN may be provided with a multicast-onlyoperating mode configured to relay the multicast data, but no unicastdata, e.g., corresponding to the above multicast-only operating mode orMBMS-only operating mode as explained above. Further, the RN may also beprovided with a mixed operating mode configured to relay the multicastdata and unicast data, e.g., corresponding to the mixed operating modeas explained above. The method may then also include switching from themixed operating mode to the multicast-only operating mode and/or viceversa. According to an embodiment, when the RN is using the mixed mode,the subframes for receiving the multicast data from the donor basestation are selected from the subframes for multicast transmission. Whenswitching from the mixed operating mode to the multicast-only operatingmode, the a handover of UEs involved in transmissions of unicast data bythe relay node to a base station, e.g., the donor base station or someother base station, or to another relay node may be initiated. Suchhandover would typically be initiated by the RN.

FIG. 14 shows a flowchart illustrating a further method according to anembodiment of the invention. The method may be used to implement theabove concepts of relaying multicast data in a base station of awireless network, e.g., in the base stations 110 as explained above.When implementing the method, it is assumed a RN of the wireless networkis configured for transmissions on the basis of a radio frame comprisingone or more subframes for unicast transmission and one or more subframesfor multicast transmission. The base station may be implicitly aware ofthis radio frame configuration or may receive a corresponding indicationfrom the RN. If the wireless network is implemented according to 3GPPLTE, the subframes for multicast transmission may be MBSFN subframes,and the base station may be an eNB. The subframes for unicasttransmission may be regular subframes.

At optional step 1410, multicast data are received by the base station,e.g., using the backhaul interface 113 of FIG. 12. If the wirelessnetwork is implemented according to 3GPP LTE, the multicast data may bereceived from an MBMS GW, e.g., the MBMS GW 130-2 of FIG. 2. Other waysof providing the base station with the multicast data may be used aswell. For example, the multicast data could be generated at the basestation. The multicast data are typically intended for multicasttransmissions to UEs, performed by the base station itself or by the RN.The multicast transmissions may be performed jointly by one or more basestations and/or one or more RNs.

At optional step 1420, synchronization information is received by thebase station. If the wireless network is implemented according to 3GPPLTE, the synchronization information may be received from an MCE, e.g.,the MCE 130-1 of FIG. 2. Alternatively or in addition, thesynchronization information may also be received together with themulticast data, in the form of time stamps included in the multicastdata. The synchronization information may be used by the base stationand/or by the RN when performing multicast transmissions jointly. Thejoint transmission may also involve other base stations or RNs. Thesynchronization information may for example define an allocation oftransport channels, e.g., of the PMCH, to subframes and/or session startinformation.

At optional step 1430, the base station transmits control information tothe RN, e.g., DL or UL scheduling information such as assignments oftime and frequency resources, information on a coding scheme to be used,and/or information on a Tx power to be used for transmissions. Thesubframes for multicast transmission may each comprise a control regionand a multicast region. The control information may be transmitted in acontrol region of a subframe for multicast transmission, in particularin a subframe used by the RN for the transmission of the multicast datafrom the RN, i.e., for a multicast transmission to UEs. As explainedabove, there may be restrictions regarding the transmission of controlinformation in such subframes. Accordingly, in some embodiments, themethod also includes that the base station receives, from the relaynode, an indication of restrictions applicable to transmission ofcontrol information in the subframes for multicast transmission. Thebase station may then control the transmission of control information tothe relay node on the basis of the received indication.

At step 1440, the multicast data and optionally also the synchronizationinformation are transmitted to the RN. The subframes for transmission ofthe multicast data to the RN, herein referred to as backhaul subframes,are selectable from the subframes for unicast transmission and thesubframes for multicast transmission.

At optional step 1450, the base station may transmit the receivedmulticast data in one or more of the subframes for multicasttransmission. As mentioned above, this may be performed jointly with theRN, some other base station and/or some other relay node. If thewireless network is implemented according to 3GPP LTE, the jointtransmission may be implemented by transmitting MBMS signals in MBSFNtransmission mode.

In some embodiments, the RN may be provided with a multicast-onlyoperating mode configured to relay the multicast data, but no unicastdata, e.g., corresponding to the above multicast-only operating mode orMBMS-only operating mode as explained above. Further, the RN may also beprovided with a mixed operating mode configured to relay the multicastdata and unicast data, e.g., corresponding to the mixed operating modeas explained above. The method may then also include that the basestation controls its operations in accordance with the operating modeused by the RN. According to an embodiment, when the RN is using themixed mode, the base station selects the subframes for transmitting themulticast data to the RN from the subframes for multicast transmission.For this purpose, the base station may receive corresponding indicationsfrom the RN. For example, the base station may receive an indicationthat the RN uses the multicast-only mode and is capable of receiving themulticast data in the subframes for unicast transmission.

It is to be understood that the methods of FIGS. 13 and 14 may becombined with each other, e.g., in a system comprising a RN operating inaccordance with the method of FIG. 13 and a donor base station operatingin accordance with the method of FIG. 14. Further, it is to beunderstood that the method steps do not need to be performed in theillustrated order, but may be rearranged or combined as appropriate.

The concepts as described above may be used for allowing standardized,i.e., inter-vendor operation of RNs with a multicast-only operationmode. Since the RN in the multicast-only operating mode may betransparent to UEs, the concepts are also useful to improve thereception of multicast data without requiring any modifications toexisting UEs. In some embodiments, it is possible to switch between themulticast-only operating mode and the mixed operating mode depending onthe network requirements, thereby efficiently balancing the needs formulticast transmissions and network service on the basis of unicasttransmissions. In other embodiments, the mixed operating mode could beomitted. For example, such embodiments could be used where coverageextension for unicast transmission is not needed, but an enhancement ofdata rates for multicast transmissions is desirable.

It is to be understood that the examples and embodiments as explainedabove are merely illustrative and susceptible to various modifications.For example, although the above description frequently mentions theexample of a wireless network according to 3GPP LTE, the concepts couldalso be applied in other types of wireless networks. Further, it is tobe understood that the above concepts may be implemented by usingcorrespondingly designed software to be executed by a processor of arelay node or base station, or by using dedicated device hardware.

1. A method of relaying multicast data in a wireless network comprisingat least one relay node, said relay node being configured fortransmissions on the basis of a radio frame comprising one or moresubframes for unicast transmission and one or more subframes formulticast transmission, the method comprising: the relay node receiving,from a base station, multicast data in one or more subframes selectablefrom the one or more subframes for unicast transmission and the one ormore subframes for multicast transmission; and the relay nodetransmitting the received multicast data in one or more of the subframesfor multicast transmission.
 2. The method according to claim 1, whereinthe received multicast data are transmitted jointly with at least onebase station and/or at least one further relay node.
 3. The methodaccording to claim 2, comprising: the relay node receiving, from thebase station, synchronization information for said joint transmission ofthe multicast data.
 4. The method according to claim 1, wherein therelay node is provided with a multicast-only operating mode during whichthe relay node is configured to relay the multicast data, but no unicastdata.
 5. The method according to claim 4, wherein the relay node isfurther provided with a mixed operating mode during which the relay nodeis configured to relay the multicast data and unicast data.
 6. Themethod according to claim 5, comprising: in the mixed operating mode,selecting the one or more subframes for receiving the multicast data inthe relay node from the one or more subframes for multicasttransmission.
 7. The method according to claim 5, comprising: uponswitching from the mixed operating mode to the multicast operating mode,initiating a handover of mobile terminals involved in transmissions ofunicast data by the relay node to the base station, to a further basestation, or to a further relay node.
 8. The method according to claim 1,wherein said one or more subframes for multicast data each comprise acontrol region (CR) for transmitting control information and a multicastregion (MR) for transmitting multicast data, and wherein the relay nodefurther receives from the base station control information in thecontrol region (CR) of said one or more of the subframes used fortransmitting the received multicast data from the relay node.
 9. Themethod according to claim 8, wherein the control information comprisesscheduling information for uplink transmissions from the relay node orfor downlink transmissions to the relay node.
 10. The method accordingto claim 8, wherein a time period for switching between said receivingof the control information and said transmitting of the receivedmulticast data extends only in the control region (CR), only in themulticast region (MR), or both in the control region (CR) and in themulticast region (MR).
 11. The method according to claim 1, wherein thewireless network is configured as a 3GPP LTE network and the subframesfor multicast transmission correspond to MBSFN subframes.
 12. A methodof relaying multicast data in a wireless network comprising at least onerelay node, said relay node being configured for transmissions on thebasis of a radio frame comprising one or more subframes for unicasttransmission and one or more subframes for multicast transmission, themethod comprising: a base station transmitting, to a relay node,multicast data in one or more subframes selectable from the one or moresubframes for unicast transmission and the one or more subframes formulticast transmission.
 13. The method according to claim 12,comprising: the base station transmitting the multicast data jointlywith the relay node in one or more of the subframes for multicasttransmission.
 14. The method according to claim 13, comprising: the basestation transmitting, to the relay node, synchronization information forsaid joint transmission of the multicast data.
 15. The method accordingto claim 12, comprising: the base station receiving from the relay nodean indication that the relay node is capable of receiving the multicastdata in the one or more subframes for unicast transmission.
 16. Themethod according to claim 12, wherein said one or more subframes formulticast transmission each comprise a control region (CR) fortransmitting control information and a multicast region (MR) fortransmitting multicast data, and wherein the base station furthertransmits, to the relay node, control information in the control region(CR) of said one or more of the subframes for multicast transmission.17. The method according to claim 12, comprising: the base stationreceiving, from the relay node, an indication of restrictions applicableto transmission of control information in the one or more subframes formulticast transmission or in the one or more subframes for unicasttransmission; and the base station controlling the transmission ofcontrol information to the relay node on the basis of the receivedindication.
 18. The method according to claim 16, wherein the controlinformation comprises scheduling information for uplink transmissionsfrom the relay node or for downlink transmissions to the relay node. 19.The method according to claim 12, wherein the wireless network isconfigured as a 3GPP LTE network and the subframes for multicasttransmission correspond to MBSFN subframes.
 20. A relay node for awireless network, said relay node being configured for transmissions onthe basis of a radio frame comprising one or more subframes for unicasttransmission and one or more subframes for multicast transmission, therelay node comprising: at least one radio interface for communicationwith a base station and one or more mobile terminals; and a processorfor controlling operations of the relay node, said operations of therelay node comprising: receiving, via the at least one radio interface,multicast data from the base station in one or more subframes selectablefrom the one or more subframes for unicast transmission and the one ormore subframes for multicast transmission; and transmitting, via the atleast one radio interface, the received multicast data in one or more ofthe subframes for multicast transmission.
 21. The relay node accordingto claim 20, wherein the relay node is configured to operate in amulticast-only operating mode during which the relay node is configuredto relay the multicast data but no unicast data, and to operate in amixed operating mode during which the relay node is configured to relaythe multicast data and unicast data, wherein in the mixed operatingmode, the relay node selects the one or more subframes for receiving themulticast data from the one or more subframes for multicasttransmission.
 22. A base station for a wireless network, wherein thewireless network comprises at least one relay node, said relay nodebeing configured for transmissions on the basis of a radio framecomprising one or more subframes for unicast transmission and one ormore subframes for multicast transmission, the base station comprising:at least one radio interface for communication with one or more mobileterminals and at least one relay node; and a processor for controllingoperations of the base station, said operations of the base stationcomprising: transmitting, via the at least one radio interface,multicast data to the at least one relay node in one or more subframesselectable from the one or more subframes for unicast transmission andthe one or more subframes for multicast transmission.
 23. The basestation according to claim 22, wherein said one or more subframes formulticast transmission each comprise a control region (CR) fortransmitting control information and a multicast region (MR) fortransmitting multicast data, and wherein the base station is configuredto transmit, to the relay node, control information in the controlregion (CR) of said one or more of the subframes for multicasttransmission.
 24. A wireless network system, comprising: a base station;and a relay node configured for transmissions on the basis of a radioframe comprising one or more subframes for unicast transmission and oneor more subframes for multicast transmission, wherein the base stationis configured to: transmit multicast data to the relay node in one ormore subframes selectable from the one or more subframes for unicasttransmission and the one or more subframes for multicast transmission,and wherein the relay node is configured to: receive the multicast dataas transmitted by the base station, and transmit the received multicastdata in one or more of the subframes for multicast transmission.
 25. Thesystem according to claim 24, wherein said relay node is configured tooperate in a multicast-only operating mode during which the relay nodeis configured to relay the multicast data but no unicast data, and tooperate in a mixed operating mode during which the relay node isconfigured to relay the multicast data and unicast data, wherein in themixed operating mode, the relay node selects the one or more subframesfor receiving the multicast data from the one or more subframes formulticast transmission, wherein said one or more subframes for multicasttransmission each comprise a control region (CR) for transmittingcontrol information and a multicast region (MR) for transmittingmulticast data, and wherein said base station is configured to transmit,to the relay node, control information in the control region (CR) ofsaid one or more of the subframes for multicast transmission.